Objectives of the study are a) to determine the effectiveness of a "deconditioning exercise" in reducing the frequency of exercise-induced asthma in children and b) to identify factors which may predict a positive response to deconditioning treatment. Definitively diagnosed asthmatic children will be tested on a standard submaximal running exercise on a treadmill. An increase of 15% or more in the total repiratory resistance after the exercise will classify those children as exercise-reactors. Forty reactors, selected in this manner, will be divided randomly into an experimental and a control group. Experimental treatment will consist of 6 minutes of exercise with or without a pre-treatment for seven sessions. Pre-treatment for experimental group will be decreasing amounts of isoproterenol inhalation during the first 5 sessions, while saline will be inhaled by the control group in the similar manner. In the 6th and 7th sessions, both groups will receive saline inhalation. This will serve as the test of the earlier procedure in the first 5 sessions. Also, the comparision of the clinical data on various parameters of asthma (e.g., frequency and duration of attack, medication, etc.), collected during 3 month baseline period, with similar post-experimental data will provide additional information on the effectiveness of the treatment.